Treating impure lead and/or tin metal



P 6, 1933- v F. REHNS TREATING IMPURE LEAD AND/OR TIN METAL Filed July 8, 1957 Al/ra/i Reading Mefa/ Pig J T 9 N M -m 1 E e f 1 C9 NI a A @w h m l nw m dY M M L A M f mm r 3 M 3 y; /)/g a ,6 ATTORNEYS Patented Sept. 6, 1938 UNIT D STATES TREATING mums man AND/R TIN METAL.

Fredrick Relms, Springfield, Masa, assignor to .The American Metal Company, Limited, New York, N. Y., a corporation of New York Application July 8, 1937, Serial No. 152,655

24 Claims.

wet drosses or crusts formed on metal baths to.

facilitate the removal thereof.

In accordance with my invention, an alkaline reacting metal, such as an ingot or other mass of an alkali or alkaline earth metal including sodium, calcium and magnesium, is incorporated 1 in a novel manner in a molten mass of tin and/or lead metal containing impurities such as, for example, antimony, arsenic, bismuth, cadmium, zlnc, gold and silver to thereby produce a compound or compounds which are subsequentlysep- 1 arated from the metals in a novel manner.

This application is a continuation in part of my copending application Serial No. 502, filed January 5, 1935.

Various other features and characteristics of my invention will become apparent from the following detailed description.

My invention resides in the art and process of refining lead and/or tin metal as herein described and claimed.

For an understanding of my invention and for an illustration of one form of apparatus suitable for the practice of my novel process, reference is to be had to the accompanying'drawing,

in which Figure 1 is a plan view illustrating the incorporation of a mass of alkaline reacting metal in a molten impure metal, and

Figure 2 is a vertical sectional view, partly in elevation, of the arrangement shown in Fig. 1. In general, the process of this invention relates to the removal from impure lead and/or tin of antimony, arsenic, zinc, cadmium and hismuth, gold andsilver. The presence in the alloy' of a small amount of copper is not harmful for the conduct of the process. However, the

amount of copper which is present should be sufflciently small to be soluble in the alloy. If this is not the case the proper execution of. the removal of antimony and other impurities may be interfered with due to removal of copper along with these impurities. v

In accordance with an important application of the invention, the metal treated by the process may be an alloy formed principally from tin and lead in amounts usually found in solder. It may I also be applied to impure lead or impure tin, mixtures of these and various white metal alloys.'

The drawing illustrates a preferred form of apparatus for practicing the process, of this in-v c5 vention. As shown, T represents an iron tank or,

kettle supported in any suitable manner, as by the structure I. Depending into the tank 'I is a shaft 2 -journaled in any suitable support which may be carried by a plurality of beams 3. Securedto the upper end of the shaft 2 is a bevel 5 gear 4 with which meshes another bevel gear 5 carried by a shaft 6 adapted to be rotated by any suitable means, not shown. The lower end of the aforesaid shaft 2 carries a suitable agitator l which, as'shown, may be of the marine screw 10 propeller type.

The metal to be treated is melted in the tank T and any dross which rises .to the top of the bath is skimmed ofi either with or without the addition of a suitable drying agent, such as rosin, 16 or sulphur and rosin according to well-known practice. While this is being done, the temperature of the molten metal should be approximately 600 F. Thereafter the molten metal is well mixed whereupon a sample is taken in order to 20 determine the copper and the metal contents of any of the other ingredients whose content it is desired to know for the purpose of reaction with the alkaline reacting metal.

At this stage of .the process the temperature 25 of the molten metal should be so adjusted that no explosive action occurs when a mass of alkaline reacting metal such as sodium, calcium or magnesium is disposed therein. This temperature will vary. For sodium it should not be above 30 600 F. and preferably such temperature should be between 500-550 F. The temperature for magnesium should be about 875 F. and the temperature for calcium and calcium-magnesium alloy hereinafter referred to should be about 35 1100' F. Thereupon the agitator l is brought up to a. rotative speed such that a good vortex is produced at thecenter of the molten metal mass. An ingot or other mass of an alkaline reacting metal designated as S is coated with a suitable 40 light fuel oil by dipping first one end of the ingot and then the other into a bath of the oil as held by a suitable container. The ingot is then placed on the surface of the moving bath of metal near the rim, of the kettle. Due to its lightness, a 45 operators.

it reaches the vortex is drawn thereinto and disappears immediately. In this way, it is possible to introduce an alkaline-reacting metal into molten lead and/or tin containing impurities without burning and, therefore, without loss and without the usual sputtering and near explosive action which occurs when such an ingot is plunged into a bath of such molten metal. When this is done, it often happens that metal spatters in all directions with attendant danger to the On the contrary in accordance with my invention the ingot gradually melts and finally disappears in the alloy mass without the occurrence of an explosion. The alkaline-reacting metal is melted progressively from the lower part of the ingotand as it melts it is carried away by Therefore, it

the more rapidly moving alloy. appears that the heat of reaction of the alkalinereacting metal with the molten metal is not localized and the temperature does not reach a point high enough to cause ignition of the ingot. The sodium or other alkaline-reacting metal as stated is melted from the, lower part of the mass and is liberated in the bath of molten metal where it,

combines quickly with the antimony and other ingredients and accordingly does not flame. The fact that the block or ingot is traveling more slowly than the mass insures the bringing of fresh material containing antimony and other impurities in contact with the molten ingot underneath the surface of the bath.

I will now describe the treatment with sodium of lead and tin in the form of solder or other white metal alloy containing antimony as principal ingredient. With a tank T having a ca pacity of from fifty to sixty tons, it is desirable that where sodium ingots are used for the removal of antimony and other impurities, they weigh approximately eleven pounds, more or less. der these conditions, as much as one drum of sodium weighing 275 lbs. net can be introduced into the molten metal in approximately seven and one-half minutes, the amount of sodium.

which is added depending, of course, upon the amount of the molten metal in the kettle and its antimony content.

As a result of the addition of sodium to the molten metal in the manner described above, an

increase in temperature of the molten metal results and this may amount to as much as F. The kettle and its contents should then stand for a time to allow the temperature thereof to drop. After about one-half hour, a wet dross starts appearing at the top of the kettle. This dross contains much more antimony than the metal underneath. However, if taken ofi in this condition, a considerable quantity of tin and lead will be mixed with it so that the antimony content ordinarily is not above approximately :5%. Therefore it is necessary to separate the sodiumantimony compound which has been formedfrom the tin and lead alloy.

To this end, I select a. suitable mineral oil of high boiling or high flash point character and one which will produce a coke as described below, such, for example, as crude Vaseline or petrolatum. Instead of crude vaseline or petrolatum, I may employ oil known as Bunker C fuel oil. This is a fuel oil having a specific gravity at 60 F. of about 0.989, a viscosity at 122 F. (Saybolt Furol) of approximately 111 seconds and an initial boiling point of approximately 450-500 F. These products are inexpensive and approximately 100 lbs. thereof are suflicient for the treatment of approximately sixty tons of molten metal having a 3% antimony content. When a product of this character is to be mixed withithe wet antimony dross, the temperature of the molten metal should not exceed approximately 500 F. This prevents the petrolatum or fuel oil from burning while being mixed into the bath in small quantitles by the agitator 1. When the dross appears to be saturated, the agitaton is stoppedfj The temperature of the moltemmetal is increased to approximately 600 F. which is high enough to ignite the petrolatum or fuel oil. At this point, the petrolatum orfuel oil starts to burn for a short time and, by a little more stirring, there is formed a very dry dross or coke-like product which is not readily wetted by the molten solder material, this dry dross being skimmed oif into drums with holes.in' the bottom which permit any adhering metal to run out.

The oil or petrolatum addition is usually repeated two or more times until no more dross comes up. In case the antimony is not reduced in the liquid metal to the desired point, more 1 sodium is added, the amount thereof depending,

on the quantity of antimony which isleft in the molten metal: This cycle is repeated until the metal has the desired low antimonycontent. I have been able to reduce the antimony content of solder material to a degree as low as .05% by this process.

My tests have indicated that the amount of sodium required varies somewhat with the antimony content of the metal being treated. With high antimony content, for example, 2% to 3%,

one pound of sodium will remove more antimony than the same "amount ofsodium will remove from metal (such as white metal alloy) of low antimony content, for example 0.5% to 0.75%.

In reducing the antimony contents-of a white metal alloy from 2% to 0.15%, the elimination of 37 lbs. of antimony per ton requires from 20 to 22 lbs. of sodium, thus eliminating on the average about'1.'76 lbs. of antimony per pound of sodium.

However, in reducing white metal alloys from 0.75% to 0.15% antimony, the elimination of 12 lbs. of antimony per ton requires about 9 to 11 lbs. of sodium, equivalent to an average of 1.20 lbs. of antimony per pound of sodium. It would seem therefore that some of the sodium is required to reach a critical point before the remainder can the tin and lead must be saturated with sodium first. In addition, I have found that in order-to reduce the antimony to the lowest point,- still now, be treated with sulphur to thereby remove such sodium as is left in said molten metal, this treatment also effecting the removal of any copper which the" solder metal may contain. Or the alloy may be heated to 700 F. and the surface sprayed with water. This reacts with part of the sodium forming sodium hydroxide and thereby decreasing the amount of dross formed when the sulphur is added. -The residual sulphur is eliminated as usual by poling or steaming.

be usefully employed to remove ant1mQny, i. -e.

Example 1 I alloy was treated in two stages with a total of 550 lbs. of sodium and 50 lbs. of petrolatum as above described, that is, 275 pounds of sodium in the first stage in the form of eleven pound ingots are melted into the alloy by floating the sodium ingots on the top exposed surface of the alloy in a spiral until the sodium reaches the vortex, passes down the vortex and is accordingly absorbed without explosion as described above. 'I'hereupon the mass is allowed to cool, 25 pounds of petrolatum are added to form a dried dross of powdery coke-like nature; the temperature is raised to about 600 F; and the petrolatum burns with a myriad of small flames and the coke-like dross is skimmed-E. This process is then repeated employing the remaining amounts of sodium and petrolatum in the same way as just described. There were produced a total of 4841 pounds of antimony skims assaying 0.25% copper, 17% antimony, 25.07% tin and 19.48% lead and 38% sodium. The bath was then allowed to cool to 500 F. when 7635 pounds of wet dross known as sodium buttons were removed. This material contained 7.49% copper, 1.42% antimony, 29.96% tin and 43.74% lead and considerable sodium. The material last named should be returned to the succeeding lot of solder material to be treated for.

. the removal of antimony in order to get the benefit of the sodium therein contained.

The alloy metal remaining in the kettles was then heated to 700 F. and the surface thereof sprayed with water to thereby form sodium hy droxide which isthen skimmed oil. Approximately 400 lbs. of sulphur were then added to the alloy metal and the dross which rose to the top was then skimmed off which removed the remainingsodium as well as the copper. From this operation, there was produced 4351 lbs. of dross assaying 4.24% copper, 0.68% antimony, 28.91% tin and 31.28% lead. The excess sulphur was then removed by blowing the alloy metal with steam which produced 385 lbs. of dross containing 0.28% antimony, 29.19% tin and 60.73% lead. There remained in the kettle 86,378,1bs. of refined solder with atrace of copper, 0.25% antimony, 32.39% tin and 67.31% lead.

The dry dross containing the antimony-sodium compound produced as described above is first liquated to separate any free solder metal which is sometimes carried with the dross in skimming. The dross is then smelted in a reverberatory furnace, with a reducing agent such as coal, to reduce all lead and antimony oxide to metal. This reduction is a well-known process. During the treatment in the reverberatory furnace suflicient heat is maintained preferably at all times to keep the slag accumulating on the top of themate rial in a substantially liquid condition. A small amount of sand shouldbe mixedv with the dross at. the time of charge into the reverberatory'fur nace to react with the sodium. This serves to protect the furnace lining. As soon as the dross is melted, a'nQoxidizing agent such as litharge is stirredinto-the bath which oxidizes the tin; the tin oxide resulting forms a dry dross containing considerable amounts of antimony and the bath. If taken off in this condition, the separation would be very incomplete. I have found that a good separation may be obtained by introducing a slagging agent, such as sand or silicious slag on the dross and melting it. The melting slag liqueiles the dross, acts as a carrier for the lead on tin oxide, releases any metallic antimony and lead which may be intermixed with it and dissolves any oxides of antimony or lead which may be present. In order to cleanse the slag produced in this way, I rabble into the slag a small amount of a reducing agent, such as coal or soft iron, the amount used being proportioned so as to reduce to metal only antimonyand lead and as little tin as possible. The treatment with the coal or other reducing agent causes the antimony and lead oxides in the slag to be reduced to the metallic state and the metal then drops to the metallic bath underneath so that the slag is freed therefrom. After the slag is treated with a reducing agent, it is tapped and may be mixed with other tin-lead drosses or similar material and smelted.

sodium compounds of these metals or as nonvolatile oxides in the metals. Any oxidized compounds will pass to the slag upon the initial heating of the dross with a small amount of sand and prior to the addition of the litharge.

Such compounds will ordinarily be in such small quantities that they would probably be thrown away. If any considerable values'are there they may be treated for their recovery. If present as .metallic compounds with sodium, these materials will be oxidized by the litharge and will follow the tin.

For the treatment of an antimony-sodium dross such as produced in'the above example containing 17% antimony and 20% tin after reduction of the same into the reverberatory or blast furnace, for each percent of tin I mixed approximately 2% or a little more of litharge. This is less than the amount theoretically required and would indicate that part of "the tin is oxidized in handling and melting. After the litharge is incorporated 20% to of the weight of the dross or sand or silicious slag is charged and melted. Then about 15-20% of soft coal of weight of slag is rabbled in. The slag as tapped assayed 26-27% SiOz (silica), '2526% Fe (iron), 40% Sn (tin), 2% Sb (antimony), with a small amount of lead. The metal produced contained 12% Sb (antimony), 1% Sn (tin) andthe balance is lead. The sodium which was combined with the antimony is contained in this slag combined with the silica with the exception of any that may have been burned'off;

Similarly I have successfully employed in' ac-,

cordance with my invention sodium for the treatment of solders containing other impurities as well as for the treatment of' 'impure lead and tin metals and I'have also successfully employed,

in accordance with, my" invention, calcium and, magnesium for removal of impurities from metals Example 2 ing arsenic andantimony from impure tin:

104.25 lbs. of tin was employed analyzing arsenic 0.99%, antimony 1.64% and tin 97.60%. The tin is melted. If any dross forms it may be removed. Sodium is added in' three stages at 9.

temperature of about 500 F. This temperature may vary somewhat according to the amount of tin employed but it usually is at a temperature of approximately to 50 F. above the melting point of the tin. The tin is'ordinarily melted in a kettle as above described provided with an agitatonand prior to the addition of the sodium the agitator is started to produce a vortex at about the center of the tin. 1.5 lbs. of metallic sodium is stirred in at 500 the sodium being floated as in Example 1. The quantity of sodium of course is less than that of a single ingot employed in the larger scale operation of Example 1 and may be introduced in the form of one or more small blocks which float on the surface of the tin and over the usual'spiral path towards the Vortex down which they disappear and are finally consumed. The temperature after this first addition of sodium is such that the sodium-arsenic and sodium-antimony compounds are dissolved in the tin and accordingly the latter should be cooled until the point is reached where this dross will come out of solution in the tin and rise to the surface. Accordingly the tin is allowed to cool to about 500 F. at which time a wet dross containing sodium, combined with arsenic and antimony, rises tothe surface. 50 grams of petrolatum is then stirred in. The petrolatum permeates the mass and causes more wet dross to rise to the surface. The temperature is then raised sumciently for the dross to dry. This will occur under these conditions at about 583 F. and at that point the petrolatum may burn and whether it burns or not a dry coke-like dross will be formed. This dross is ready for removal. It is removed and the second addition of sodium made. After removal of the dross the metal analyzed arsenic 0.06%, antimony 0.96% and tin 98.60%. For the second addition of sodium 1 lb. was employed and floated with stirring on the kettle and after the sodium was consumed the temperature was allowed again to fall to permit the separation of the sodium-arsenic and sodium antimony compounds. Thereupon a further addition of 35 grams of petrolatum was made with stirring and the temperature raised again to approximately 583 F. to form a second dry dross. After this second treatment. an analysis of the metal showed arsenic none, antimony 0.27% and tin 99.78%. In order to remove the residual antimony, a third addition of ,4 lb. of sodium was made and the metal cooled to about 500 F. grams of petrolatum was then added, the temperature again raised to 583 F. and the dross removed. The antimony content of the metal after this third addition was 0.03%, the balancebeing tin. The final purified tin weighed 73.97 lbs., the total dross weighed 28.56 lbs. The total amount of sodium employed was 3 lbs. The total amount of petrolatum used was 110 grams.

The residual sodium was removed from the final tin obtained by raising the temperature to approximately 700 F. and treating the mass with water whereupon the sodium and water react to form sodium hydroxide substantially free from water which was removed by skimming.

The dross containing arsenic, antimony and tin may be reduced in a reverberatoiy or blast furnace as in Example 1; after addition of a small.

In' order to separate these For each perporated 20 to 25%oftheweight of the dross in sand or silicious slag is charged and melted. After. the slag is treated with the reducing agent it is tapped and may be mixed with other tin drosses and smelted. The metallic lead produced by the reaction of the tin and lead-oxide above collects below the slag. along with the antimony and whatever arsenic remains and this "antimonylead alloy may be worked up to form antimony or lead orantimonial lead as desired.

3 Example 3 The following is a typical example for removing arsenic from tin:

The removal of arsenic from tin follows in general the procedure given in Example 2. It may be accomplished by one treatment with sodium where the quantity of arsenic is small say 1% or less, but if the amount of arsenic is higher than this two or more treatments with sodium and petrolatum may be necessary. 102 lbs. of tin analyzing 0.46% arsenic and 99.53% tin are melted and any dross removed by skimming. The molten metal at a temperature of say 500 F. -preferably 20 to 50 or above the melting point of the tin-is treated with 1 lb. of sodium by floating in a kettle provided with an agitator as indicated in Example 2. The metal is cooled and the wet dross of the sodium-arsenic compound rises to the surface. 56 grams of petrolatum are stirred in at approximately 580 F. and a dry coke-like dross formed ordinarily with incidental burning of the petrolatum. The quantity of treated tin obtained was approximately 82.75 lbs., the analysis for arsenic showed none present.

The residual sodium in the tin obtained may be removed as in Example 2.

The dross containing the sodium-arsenic compound and tin may be treated in order to recover the tin in any desired manner.

Example 4 The following is a typical example for removal of antimony from tin:

The procedure here is also similar to that in Example 2 above. 103 lbs. of tin containing 0.94% antimony and 99.05% tin is melted and any dross rising is skimmed off. The metal is treated at 20-50 above its melting point, say 480 F. with approximately 1.75 lbs of sodium by floating the sodium and stirring as described 'formed and removed. The treated metal weighs 79.75 lbs. and shows an antimony content or analysis of 0.03%. The dross removed contain- -ing the antimony shows an analysis 8.27% and 74.90% tin.

The residual sodium in the tin may be' removed as described in Example 2. The dross may be treated in any desired manner'to recover the tin and antimony therefrom.

Example The following is a typical example of the removal of bismuth from solder with sodium and petrolatum:

This solder mixture is treated similarly to that in Example -1. The mixture containing tin 38.90%, arsenic 0.025%, antimony 0.41%, bismuth 0.70% and the balancelead is melted and any dross rising is skimmed off. The solder is given a two-stage sodium-petrolatum treatment. In the first stage the sodium is added at a temperature of about 20-50 F- above the melting point of the -solder, namely at about 500 F. 184.8 lbs. of such solder is treated with 1.3 lbs. of sodium by floating in a vessel with an agitator as described above. After addition of the sodium the mass is allowed to cool until a wet dross separates. Approximately 50 grams of petrolatum are added and the temperature raised to about 583 F. to form a dry dross with incidental burning of the petrolatum. The resulting metal weighed 175.51 lbs. and the dross 6.87 lbs. After treatment of the metal it analyzed arsenic 020%, antimony 0.30%, bismuth 0.41%, tin 39.01% and the balance lead. The dross contained 29.40% lead, arsenic none, antimony 3.82%, bismuth 1.07% and tin 24.50%. In the second stage of the treatment with sodium, to

the molten metal wasadded 1.49 lbs. of sodium with stirring as before. The temperature was allowed to drop to approximately 500 F. About 70 grams of petrolatum were added and the temperature raised to about 583 F. with incidental burning of the petrolatum and formation of the dry coke-like dross. Afte? this second treatment of the antimony metal showed antimony 0.075% and bismuth 0.17%. The dross contained 3.11% of antimony, 1.14% of bismuth, 31.1% of tin and 41.8% of lead. In accordance with this procedure it was found that antimony and bismuth are removed at the same time and the antimony has the preference at very low percentages, that is more antimony than bismuth is removed by the process when the percentages of these metals are low.

The resulting treated metal contains some residual sodium which may be removed by treatment with. water as in Example 1. Any copper present may also be removed by treatment with sulphur as in Example 1.

.The combined dross contained metallic com pounds of sodium and the following metals arsenic, antimony, bismuth, tin and lead and oxides of these combinations. ed as in Example 1 by smelting it in a reverberatory or blast furnace with addition of a small amount of sand and coal. metal a separation may be effected by the addition of litharge in the amount of approximately 2% or a little more of litharge for each percent of tin present. After the litharge is incorporated 20-25% of the weight of the dross of sand or silicious slag is charged and melted. The litharge converts the tin to oxide and also converts the sodium to sodium-oxide, .there being just sumcientlitharge added for this purpose. Upon addition of the sand, the sodium-oxide combines therewith to form a liquid slag which picks, up

of antimony v This dross may be treat- After reduction tothe tin-oxide. The remaining ingredients, namely lead, antimony, arsenic and bismuth, drop to the bottom of the bath and are recovered as metals. They maybe separated as desired. The tin being skimmed off as dross contains also litharge and smaller amounts of antimony and small amounts of bismuth and other metals as oxides. This dross .is smelted to reduce these oxides to metal. tains substantially all of the tin removed during the process of treatment of the solder metal with sodium. Minor amounts of other metals maybe removed from the tin by well known processes.

Similarly in accordance with my invention I may treat tin, containing cadmium and/or zinc as impurities with sodium to remove cadmium and/or zinc therefrom in a similar manner.

Similarly magnesium may be employed instead of sodium for the removal from lead and/or tin of antimony, arsenic, cadmium, zinc, bismuth,

gold and silver. Similarly I may employ other low-melting point alkali metals such as potassium, but potassium is not commercially practical at the present time because of its high cost. Calcium will also react with antimony, arsenic, zinc, cadmium, bismuth, gold and silver, to produce a dross which may be dried and removed as described in the case of sodium.

I prefer to employ in accordance with results that I have secured in actual practice a calciummagnesium alloy having a calcium content ofabout 20.6% and magnesium content of about 79.4%, which calcium-magnesium alloy can be floated on the surface of the metal baths to be purified as mentioned above in the same manner' as herein described for sodium. The following are specific examples of the use of alkaline earth metal employing the preferred calciummagnesium alloy mentioned.

Example 6 The removal of bismuth and gold and silver from impure lead by floating a calcium-magnesium alloy thereon is illustrated by the following example:

Into 210 pounds of antimonial lead, containing gold 0.82 oz./ton;'silver 90 ozs./ton; antimony 5.80%; bismuth 2.95%; and small amounts of copper, arsenic and tin, 6 pounds of a calcium (20.6%) magnesium v(79.4%) alloy were introduced by floating at 1100 F. with a propeller agitator as hereinabove described." A dross was formed which was skimmed. The dross does not require drying by petrolatum or the like since it'is sufficiently dry for removal as it forms. It contained gold and silver 805.2 ozs./ton; antimony 1.35%; bismuth 27.26%. The metal after treatment contained by analysis gold plus silver 18.2 ozs./ton; antimony 5.55%; bismuth 0.45%.

' Example 7 I have also demonstrated that petrolatum may The metal thus obtained conbe used to advantage when calciumor magnesium is introduced into the metal in the usual way, i. e.,'

of petrolatum were used.

The introduction of calcium in accordance with Example 7 is made by immersion of the calcium beneath the surface of the molten metal bath. Where the calcium or calcium-magnesium alloy is floated on such a bath it is necessary to raise the bath to a higher temperature, namely to about 1100 F. Under such conditions the alkaline earth metals will float and be consumed by the impurities of the bath which react therewith. After the alkaline earth metals have been introduced in this manner and a wet dross is obtained which it is desired todry by petrolatum or other high boiling oil, these can be satisfactorily introduced but it is necessary prior to their introduction to cool the bath to a temperature of about GEO-700 F. After the petrolatum has been introduced by stirring with the propeller agitator in the usual way, the temperature of the bath should be raised so thatthe petrolatum or oil is ignited or will be burned in the usual manner with a myriad of small flames. A suitable temperature for this is about 725 F. After the small flames have ceased burning the dross will be dried and will be skimmed off in the usual manner.

I have also found in accordance with my invention that various other drosses than those described in the above examples may be dried by means of the addition of a high boiling oil with subsequent coking to render the dross dry. I have found that lead and tin containing copper when treated with sulphur will producea wet dross containing copper and that this may be dried in a similar manner by the addition of a high boiling oil and coking. Similarly I have found that the wet silver-zinc crust obtained in the removal of silver from lead by the wellknown zincing process may also be dried in a similar manner according to my invention. The following are further specific examples of such drying processes.

Example 8 moved showed a copper content of 20.66%.

Example 9 215 pounds of lead containing 375 ozs. of silver per ton was melted in a kettle and zinc added in the usual way. A wet silver-zinc crust was formed. A propeller agitator was put in the kettle and 175 grams of petrolatum stirred in during a period of 10 minutes while the temperature of the bath was about 793 F. The petrolatum burned as usual and a dry dross formed and was skimmed off. A sample of the dross assayed 13,700 ozs. silver per ton.

After the addition of the petrolatum or other like oil and heating of the kettle in practising the invention, for instance in accordance with any of the Examples 1-9, it is not necessary to stop the heating at a temperature where the dry dross 2,129,445 bismuth and the dross 4.22% bismuth. 145 grams has first formed. At that point the compounds obtained will usually not be in the oxide form but they will be dry. 'If the heating is continued the dross may be even drier than at the lower temperatures since practically all of the substances present will be present as oxides.

The term alkaline-reacting metal as used in the appended claims is intended to designate an alkali metal or an alkaline earth metal, capable of reacting with impurities, for example antimony, arsenic, bismuth, cadmium, zinc, gold and silver to produce a compound or compounds.

While I have described my improvements in great detail and with respect to certain preferred embodiments thereof, I do not desire to bellmited to such details or embodiments, since many changes and modifications may be made and the invention embodied in widely different forms without departing from the spirit and scope thereof in its broader aspects. Hence I desire to cover all equivalents and all modifications and forms coming within the language or scope of any one or more of the appended claims.

What I claim as new and desire to secure by Letters Patent is:

1. In the art of treating impure lead and/or tin metal, the step which consists in floating and causing relative motion between an alkaline-reacting metal and the surface of said impure metal in molten condition and thus causing a reaction between the alkaline-reacting metal and impurity or impurities at a rate such that the heat of reaction is not localized, whereby said metal is gradually incorporated in the impure metal with out ignition, to form a removable dross containing the impurity or impurities.

2. In'the art of treating impure lead and/or tin metal, the step which consists in floating and causing relative motion between an ingot of sodium and the surface of said impure metal and thus causing a reaction between the sodiumingot and the impurity orimpurities at a rate such that the heat of reaction is not localized whereby said alkaline-reacting metal is gradually incorporated in the impure metal without ignition, to form a removable dross containing the impurity or impurities. v

3. In the art of treating impure lead and/or tin metal, thestep which consists in producing relative movement between an alkaline-reacting metal having a. protective coating but affording contact with an exposed surface of said impure metal.

4. In the art of separating impurities from metal in an impure lead and/or impure tin, the step which consists in producing relative movement between a mass of oil-coated alkaline-reacting metal in contact with an unconfined surface of the impure metal.

5. In the art of treating impure lead and/or tin metal, the process which comprises producing relative movement between an alkaline reacting metal having a protective coating in contact with an unconfined surface of said impure metal to produce a dross containing a compound of said alkaline reacting metal and one or more of said impurities, and treating said dross with a high boiling oil to thereby form a coke-like substance containing said compound.

6. In the art of treating impure lead and/or tin metal, the step which consists in stirring the molten metal to thereby produce movement of a mass of protectively coated sodium floated on the impure metal surface.

7. In the art of treating impure lead and/or tin metal, the steps which consist in applying to said metal in molten condition held in a vessel, a stirringforce of sufficient intensity to produce a vortex near the center of said vessel, and disposing a mass of alkaline reacting metal on the surface of said impure metal adjacent the vessel wall, said mass of alkaline reacting-metal fioating on the surface of said molten metal and moving generally along a spiral path toward the center of the vessel and then passing downwardly into said vortex.

8. In the art of separating antimony and/or arsenic from tin metal, the step which consists in producing relative movement between a mass of sodium in contact with an exposed surface 6f the molten tin while maintaining it at a temperature of about 470-500" F.

9. In the art of separating bismuth, arsenic and antimony from lead and tin, the step which consists in producing relative movement between a mass of sodium in contactwith an exposed surface of the molten lead, tin, arsenic, antimony and bismuth, while maintaining it at a temperature of about 500 F.

10. In the art of separating bismuth from lead containing it as an impurity, the step which consists in producing relative movement between a mass of calcium in contact with an exposed surface of the lead containing bismuth, while maintaining it at a temperature of about 800-835 F.

11. A process for treating lead and/or tin containing at least one of the impurities, antimony, arsenic, bismuth, cadmium and zinc, which comprises forming a wet dross, containing a compound of an alkaline reacting metal with one or more of said impurities, mixing a high boiling oil with the wet dross and then burning said-oil from the surface of the molten metal, whereby the wet dross forms a dry coke-like substance which can be readily removed.

12. In the art of treating impure lead and/or tin metal, containing antimony and possibly copper, the process which comprises floating sodium on the surface of the metal, adding a high-flash coking oil to form a dry coke-like dross containing the sodium antimony compound, removing the dry dross, and treating the molten metal to remove sodium and any copper.

13. In the art of treating lead and/or tin metal, containing antimony, the process which comprises combining sodium with the metal while the latter is molten, stirring a high-flash coking oil into the molten metal, burning the oil from the surface of the molten metal to thereby form a dry coke-like dross containing the sodiumsodium-removing agent.

14. In the art of separating antimony from a solder containing lead and tin as principal ingredients along with the antimony, the process which comprises combining sodium with the solder while the latter is molten, stirring a highflash coking oil into the molten solder, burning the oil from the surface of the molten solder to thereby form a dry coke-like dross containing the sodium antimony compound, removing the dry dross, cooling the mass, allowing further wet dross to rise to the surface, removing the wet dross, and treating the molten solder to remove sodium and any copper. Q

15. In the-art of separating antimony from a solder containing lead and tin as principal ingredients along with the antimony, the process which comprises successively combining individual masses of sodium with the solder while the latter is molten, stirring a high-flash coking oil into the molten solder, increasing the temperature of said molten solder to: burn the oil and form a dry coke-like dross containing the sodium-antimony compound, removing the dry dross and repeating the treatment with sodium and oil if necessary'until the compound of antimony is sufliciently reducedycooling the mass, allowing further wet dross to rise to the surface, removing the wet dross, treating the molten solder remaining with sulphur to remove sodium and any copper, and steaming the solder to re move residual sulphur.

16. In the art of separating antimony from a solder containing lead and tin as principal ingradients along with the antimony, melting the solder, removing dross therefrom, floating sodium on the surface of the solder, adding slowly a high flash coking oil to form a dry coke-like dross containing the sodium antimony compound, removing the dry dross and repeating the treatment with floating sodium and oil if necessary until the compound of antimony is sufficiently reduced, cooling .the mass, allowing further wet dross to rise to the surface, removing the'wet dross, treating the molten solder metal remaining with sulphur to remove sodium and any copper, and steaming the solder to remove residual sulphur.

17. In the art of separating antimony from a molten white metal alloy containing lead and tin as principal ingredients along with the antimony, the process which comprises combining sodium with said metal alloy to produce a dross containing a sodium-antimony compound, treating said dross with a'high boiling oil to thereby form a coke-like substance-containing said compound, removing said dross from the surface of said metal alloy and melting the same, adding an oxidizing agent to the molten dross material to thereby produce tin oxide in the form of a dry dross containing antimony and lead, adding sand or silicious slag to the last named dross, melting said last named dross to release metallic antimony and lead from the tin oxide, and treating the resulting slag with a reducing agent to reduce any antimony and lead oxides present.

18. In the art of treating impure lead and/or tin metal, the step which consists in floating and causing relative motion between a calcium-magnesium alloy and a surface of said impure metal in molten condition at a temperature of about 1100 F. and thus causing reaction between calcium-magnesium alloy and impurity or impurities at a rate such that the heat of reaction is not localized and the metal is gradually incorporated in the impure metal without ignition to form a removable dross containing the impurity or impurities.

19. A process for treating impure lead and/or tin metal, which comprises floating an alkaline earth metal on the surface of said impure metal in molten condition and thus causing reaction between the alkaline earth metal and; impurity or impurities at a rate such that the heat of reaction is not localized, to form a wet dross containing the impurity or impurities, mixing a high boiling oil with the wet dross and then burning said oil from the surface of the metal whereby the wet dross forms a dry coke-like substance which can be readily removed.

20. A process of the kind described which comprises mixing a high boiling oil with a wet dross containing calcium and then burning said oil line earth metal and the surface of said impure lead in molten condition thus causing a reaction between said alkaline earth'metal and impurity or impurities to form a dross containing the gold and silver, and removing said dross.

I 22. A process of the kind described, which comprises mixing a high boiling oil with wet dross on a bath of molten metal at a temperature below the ignition point of said oil, whereby saidv oil with attached dross rises to the surface of the bath, and then partially burning the oil at the surface of the bath by raising the temperature thereof. whereby the wet dross forms a dry cokelike substance which can be readily removed.

23. A process of the kind described, which com- "prises mixing a high boiling oil with wet silver zinc crust at a temperature below the ignition point of said oil, whereby said oil with attached dross then rises to the surface of the bath, and then partially burning the oil at the surface of the bath by raising the temperature thereof, whereby the wet crust forms a dry coke-like substance which can be readily removed.

24. A process for treating leadand/or tin metal containing copper, which comprises mixing sulphur with such molten metal, forming a wet dross containing a compound of copper and sul phur, mixing a high boiling oil with the wet dross at a temperature below the ignition point of said oil, whereby said'oil with attached dross then rises to the surfaceof the bath, and then partially burning the oil at the surface of the bath by raising the temperature thereof, whereby the wet dross forms a dry coke-like substance which can be readily removed.

' FREDRICK REHNS. 

